Patent GB-959106-A (GB)
Title: Improvements in or relating to radio direction finders
Inventor: BYATT DENNIS WILLIAM GEORGE
IPC: G01S3/50
Filed: 1961-05-15
Abstract: 959,106. Direction finding. MARCONI CO. Ltd. April 2, 1962 [May 15, 1961], No. 17570/61. Heading H4D. In a radio direction finder the direction of a transmitting modulated signal source is determined by demodulating and differentiating the signals received therefrom at two fixed spaced points, to produce two differentiated resultant signals and measuring and/or utilizing the time interval between the occurrence in the said resultant signals of the first resultant produced by a given part of the transmitted signal. In the embodiment of Fig. 1, a keyed H.F. transmission is received at the widely separated aerials 1a and 1b, which may be directional, having the envelope waveform of Fig. 2a, A being the front of the initial keyed pulse whilst B, C . . . F, represent reflected interference pulses. The thus received signal at 1a is amplified in 2 and transmitted to the aerial 1b site by a microwave radio link, comprising a microwave modulator/transmitter 3, sending and receiving aerials 4 and 5 and receiver/ demodulator 6. The two H.F. signals thus obtained from aerial 1b and indirectly from aerial 1a are applied respectively together with outputs from a local oscillator 9 to demodulators 8 and 7 to give the waveform of Fig. 2a. The resulting two outputs are fed, in the switch positions shown, to differentiators 11 and 10 to produce output signals as in Fig. 2b. The initial pulse A<SP>1</SP> in the output from differentiator 11, which, by virtue of the radio link between the two aerials, always leads that from the differentiator 10, is used to trigger the time base 14 of a double beam C.R.T. 15, such that the two outputs are displayed on the C.R.T. as in Fig. 2c, the lower trace, representing the output from differentiator 10, lagging behind that from differentiator 11 by a time interval representing the difference in the distance of the two aerials 1a and 1b from the transmitting source and therefore the direction of the source. The period of the time base scan is so chosen that it is not retriggered by any of the reflection pulses B<SP>1</SP> ... F<SP>1</SP>. Where an audio frequency modulated H.F. transmission is received by the two aerials, audio components having a period less than the time base period give rise to incorrect operation and to overcome this all frequencies above say 1000 c/s. are filtered out of the H.F. signal envelope by filters 16 and 17 in the second position of the switches. The remaining audio frequency signals and the associated reflection signals are squared in 18 and 19 before differentiation. In a second embodiment, Fig. 4 (not shown), the signal transmitted by the radio link from aerial la to the aerial 1b site is an intermediate frequency signal obtained by heterodyning with oscillations produced at the aerial 1b site and transmitted to the aerial la site by a second radio link which may also be used to transmit remote control signals. The time interval and/or the direction of the source may be read off the C.R.T. by a cursor or by a calibrated horizontal shift control or by a magnetic drum having a movable recording and/or reproducing head which may be provided in the path from amplifier 13 and adjusted until the two traces coincide wherein the bearing can be read of the adjustment member of the magnetic drum. The C.R.T. may be a direct view storage tube to enable short duration signals to be used whilst the source of the incoming signals may be determined by any known means.